Collaboration and License Agreements - Additional Information (Details)				1 Months Ended								3 Months Ended				9 Months Ended
	Mar. 25, 2021 USD ($) $ / shares	Feb. 14, 2021 USD ($) program	Apr. 29, 2020 USD ($) Unit $ / shares shares	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($) shares	Sep. 30, 2019 USD ($)	Aug. 31, 2019 USD ($)	Sep. 30, 2018 USD ($)	Jul. 31, 2018 USD ($)	May 31, 2018 USD ($)	Oct. 31, 2017 USD ($) shares	Mar. 31, 2021 USD ($) shares	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020	Dec. 31, 2020 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Current deferred revenue												$ 262,929,000					$ 6,451,000
Contract asset												112,500,000
Research and development												$ 134,870,000		$ 64,979,000
2020 Stock Purchase Agreement | GGL
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Issuance of common stock, shares | shares			6,626,027
Share purchase price per share | $ / shares			$ 37.73
Issuance of common stock, value			$ 250,000,000.0
Preliminary Collaboration Agreement | 2020 GSK
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of years conduct certain research and development activities under mutually agreed development plans			4 years
Maximum percentage of right to perform details in connection with antibody product			20.00%
Termination description												Either party has the right to terminate the 2020 GSK Agreement in the case of the insolvency of the other party, an uncured material breach of the other party with respect to a collaboration program or collaboration product, or as mutually agreed by the parties.
Number of units of account | Unit			4
Additional research and development expense												$ 18,500,000
Preliminary Collaboration Agreement | 2020 GSK | Accrued and Other Liabilities
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payable												13,600,000
Preliminary Collaboration Agreement | 2021 GSK
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of years conduct certain research and development activities under mutually agreed development plans		3 years
Number of separate programs | program		3
Percentage of share development costs		50.00%
Percentage of share Profit and loss		50.00%
Upfront payment receivable		$ 225,000,000.0
Percentage of upfront payment receivable at effective date of agreement		50.00%
Option exercise fee to be received		$ 300,000,000.0
Fixed consideration		$ 112,500,000
Percentage of upfront fee		50.00%
Premium paid on sale price of common stock		$ 34,800,000
Remaining upfront fee												112,500,000
Current deferred revenue												259,800,000
Receivable from collaboration												112,500,000
Contract asset												112,500,000
Research and development												$ 0
Preliminary Collaboration Agreement | 2021 GSK | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Pre-defined regulatory milestone payment		$ 200,000,000.0
Preliminary Collaboration Agreement | Antibody Program | 2020 GSK
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of development costs			72.50%
Antibody license transaction price			$ 43,300,000
Total revenue													$ 43,300,000
Preliminary Collaboration Agreement | Vaccine Program | 2020 GSK
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of development costs			27.50%
2020 Preliminary Collaboration Agreement and Stock Purchase Agreement | GGL | ASC 606
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Fair market value of the common stock issued			$ 206,700,000
Common stock price per share | $ / shares			$ 36.70
Premium received on sale price of common stock			$ 43,300,000
Definitive Collaboration Agreement | 2021 GSK
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of upfront payment receivable at effective date of agreement		50.00%
2021 Stock Purchase Agreement | GGL
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Issuance of common stock, shares | shares												1,924,927
Common stock to be issued, value		$ 120,000,000.0
2021 Preliminary Collaboration Agreement and Stock Purchase Agreement | GGL | ASC 606
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Fair market value of the common stock issued	$ 85,200,000
Common stock price per share | $ / shares	$ 52.70
Premium received on sale price of common stock	$ 34,800,000
Brii Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Termination description												Each party may terminate for convenience all rights and obligations with respect to any program for which it has an option, with 30 days’ written notice (if the terminating party has not exercised an option for such program) or 180 days’ notice (following the exercise of an option for such program). The Brii Agreement may also be terminated by either party for insolvency of the other party, and either party may terminate the Brii Agreement in its entirety or on a program-by-program basis for the other party’s uncured material breach on 60 days’ written notice (or 30 days’ notice following failure to make payment).
Written notice period for not exercising an option										30 days
Written notice period for exercise an option										180 days
Written notice period for uncured material breach										60 days
Written notice period for failure to make payment										30 days
Brii Agreement | Brii Bio Parent
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of ordinary share equal to outstanding share										9.90%
Option exercise fee ranging from mid-single-digit				$ 20,000,000.0									20,000,000.0
Sales milestone receivable				175,000,000.0									175,000,000.0
Contract liability				2,700,000									2,700,000
Option exercise fee received				20,000,000.0
Determined transaction price				22,700,000
Brii Agreement | Brii Bio
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Royalty payment obligation expiration period after first commercial sales												10 years
Contract liability										$ 3,800,000
Brii Agreement | Brii Bio | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Option exercise fee ranging from mid-single-digit										20,000,000.0
Option exercise fee of ranging from low tens										50,000,000.0
Brii Agreement | Brii Bio | Maximum | China Territory
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Sales milestone receivable										175,000,000.0
Brii Agreement | Brii Bio | Maximum | United States
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Sale milestone payments										175,000,000.0
Brii Agreement | Brii Bio | Other Assets
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Carrying value of investment												$ 5,700,000					$ 5,700,000
Brii Agreement | Alnylam Pharmaceuticals Inc | Research and Development Expense
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from options exercised													10,000,000.0
Brii Agreement | Licensed Product-By-Licensed Product | Brii Bio Parent
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payment on basis ranging from mid-single-digit				30,000,000.0									30,000,000.0
Brii Agreement | Licensed Product-By-Licensed Product | Brii Bio | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payment on basis ranging from mid-single-digit										30,000,000.0
Milestone payment on basis of ranging from low tens										$ 100,000,000.0
Brii Agreement | Biological Materials | Brii Bio Parent
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total revenue												$ 400,000
Brii Agreement | License | Brii Bio Parent
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total revenue													22,700,000
Alnylam Agreement | Alnylam Pharmaceuticals Inc
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Issuance of common stock, shares | shares					1,111,111						1,111,111
Termination description												The Company may terminate the Alnylam Agreement on a program-by-program basis or in its entirety for any reason on 90 days’ written notice. Either party may terminate the agreement for cause for the other party’s uncured material breach on 60 days’ written notice (or 30 days’ notice for payment breach), or if the other party challenges the validity or enforceability of any patent licensed to it under the Alnylam Agreement on 30 days’ notice.
Royalty payment obligation expiration period after first commercial sales												10 years
Written notice period for exercise an option											90 days
Written notice period for uncured material breach											60 days
Written notice period for failure to make payment											30 days
Upfront fee paid											$ 10,000,000.0
Recognized liability											$ 800,000
Maximum shares to be issued | shares											1,111,111
Written notice period for licensed program other party challenges validity or enforceability of patent license.											30 days
Estimated fair value of the derivative liability					$ 29,200,000									29,200,000
Contractual payments													15,000,000.0
Milestone payments paid.														15,000,000.0
Change in fair value of Milestone Shares												$ 16,800,000
Expenses incurred under agreement												$ 900,000		2,300,000
Alnylam Agreement | First siRNA product | Alnylam Pharmaceuticals Inc
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum milestone payment for achievement of specified development and regulatory											$ 190,000,000.0
Alnylam Agreement | Each Infectious Disease siRNA | Alnylam Pharmaceuticals Inc
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum milestone payment for achievement of specified development and regulatory											115,000,000.0
Alnylam Agreement | Commercialization | Alnylam Pharmaceuticals Inc
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum sales milestone payment											100,000,000.0
Maximum aggregate sales milestone payment											$ 250,000,000.0
Development and Manufacturing Collaboration Agreement | WuXi Biologics
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Termination description												the WuXi Biologics Collaboration Agreement may be terminated by (i) the written agreement of both parties, (ii) WuXi Biologics following the one year anniversary of the WuXi Biologics Collaboration Agreement effective date with respect to the entire agreement or on a product by product basis with 90 days’ prior written notice or (iii) by either party if the other party materially breaches the WuXi Biologics Collaboration Agreement and fails to cure such breach within sixty days.
Rockefeller Agreement | Rockefeller
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Termination description												The Company has the right to terminate the Rockefeller Agreement in its entirety, or in part, for any reason on 60 days’ written notice to Rockefeller. Rockefeller may terminate the Rockefeller Agreement on 90 days’ written notice for the Company’s uncured material breach, or if the Company challenges the validity or enforceability of any of the licensed patents, or immediately in the event of the Company’s insolvency. Rockefeller may also terminate the Rockefeller Agreement if the Company ceases to carry on business with respect to the rights granted to the Company under the agreement.
Upfront fee paid									$ 300,000
Royalty obligation period from date of first commercial sale																12 years
Rockefeller Agreement | Commercialization | Rockefeller
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment of annual license maintenance fees									1,000,000.0
Rockefeller Agreement | First Infectious Disease Product | Rockefeller
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum milestone payment for achievement of specified development and regulatory									$ 80,300,000
Rockefeller Agreement | HBV Program | Rockefeller | Research and Development Expense
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Specified development milestones and annual license maintenance fees													$ 1,300,000
License maintenance fees												$ 0		$ 0
MedImmune Agreement | MedImmune
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Termination description												The Company may terminate the MedImmune Agreement in its entirety or on a product-by-product basis, for convenience, upon 120 days’ notice. Either party may terminate the MedImmune Agreement for cause for the other party’s uncured material breach on 60 days’ notice or immediately in the event of bankruptcy of the other party. Additionally, MedImmune may terminate the MedImmune Agreement for cause on 30 days’ written notice if the Company challenges the validity or enforceability of the patents to which the Company has obtained a license under the MedImmune Agreement.
License agreement upfront payment								$ 10,000,000.0
MedImmune Agreement | Influenza A and Influenza B | MedImmune
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development, regulatory, and commercial milestone payments maximum amount								$ 331,500,000
Development, regulatory, and commercial milestone payments															$ 5,000,000.0
2019 Xencor Agreement | Xencor
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Termination description												The Company may terminate each agreement in its entirety, or on a target-by-target basis, for convenience upon 60 days’ written notice. Either party may terminate each agreement for the other party’s uncured material breach upon 60 days’ written notice (or 30 days in the case of non-payment) or in the event of bankruptcy of the other party immediately upon written notice. Xencor may terminate each agreement immediately upon written notice if the Company challenges, or upon 30 days’ written notice if any of the Company’s sublicensees challenge, the validity or enforceability of any patent licensed to the Company under each respective agreement.
Written notice period for uncured material breach												60 days
Written notice period for failure to make payment												30 days
Written notice period for termination of licensed program												60 days
Written notice period for termination of licensed program based on challenge												30 days
2019 Xencor Agreement | Influenza A Research Programs | Xencor
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum aggregate development and regulatory milestone payments							$ 17,800,000
Maximum aggregate commercial sales milestone payments							60,000,000.0
Maximum aggregate milestone payments							77,800,000
Specified development milestones payment						$ 800,000
2019 Xencor Agreement | HBV Research Programs | Xencor
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum aggregate milestone payments							77,800,000
Specified development milestones payment				$ 300,000
2019 Xencor Agreement | Influenza A and HBV Research Programs | Xencor
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum aggregate milestone payments							$ 155,500,000
2020 Xencor Agreement | Xencor
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Termination description												The Company may terminate each agreement in its entirety, or on a target-by-target basis, for convenience upon 60 days’ written notice. Either party may terminate each agreement for the other party’s uncured material breach upon 60 days’ written notice (or 30 days in the case of non-payment) or in the event of bankruptcy of the other party immediately upon written notice. Xencor may terminate each agreement immediately upon written notice if the Company challenges, or upon 30 days’ written notice if any of the Company’s sublicensees challenge, the validity or enforceability of any patent licensed to the Company under each respective agreement.
Written notice period for uncured material breach												60 days
Written notice period for failure to make payment												30 days
Licensed patents expiration period												12 years
Written notice period for termination of licensed program												60 days
Written notice period for termination of licensed program based on challenge												30 days